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Chapter 15 Human Influences on Climate Figure CO: Chapter 15, Human Influences on Climate--Air pollution in New York City © Dean D. Fetterolf/ShutterStock, Inc. Feedback: change leads to change leads to more change • Positive feedback mechanism: reinforces (enhances) the original trend (change) • Negative feedback mechanism: damps out an existing trend (change) • Example of a positive feedback mechanism: warming, evaporation, water vapor, warming More climate feedback mechanisms • Example of a negative feedback mechanism: warming, evaporation, water vapor, cloud, cooling • Another positive feedback mechanism: – Called the ice/albedo feedback mechanism – Cooling, more ice, higher albedo, more cooling – Warming, less ice, lower albedo, more warming Figure 01: Ice Albedo Feedback Air Pollution • Air pollutants are aerosol particles (liquids and solids) and gases that, in high concentrations, seriously affect the lives of people and animals, harm plants, or threaten ecosystems. • Air pollutants can come from natural sources (volcanoes, forest fires, dust storms) or human activities (anthropogenic sources) Figure 02: CO in lower troposphere – satellite image Courtesy of NASA Anthropogenic Sources of Air Pollution • Transportation: motor vehicles, aircraft, ships • Energy generation: electricity generation • Industry: smelting, dry cleaning, manufacturing • Home heating Carbon dioxide can be considered a pollutant Primary Air Pollutants • Emitted directly by sources • Carbon monoxide, a gas, incomplete combustion, can cause death in small concentrations, emitted by vehicles and defective heating devices • Lead, a particulate, brain damage, in some paints and treated gasoline, outlawed now More Primary Air Pollutants • Oxides of sulfur, sulfur dioxide and sulfur trioxide, respiratory irritant, emitted in burning fossil fuels containing sulfur • Oxides of nitrogen, nitric oxide and nitrogen dioxide, pulmonary problems, emitted by high-temperature combustion of fossil fuels in transportation and electric energy generation More Primary Air Pollutants • Hydrocarbons, also called volatile organic compounds, or VOCs – Some are carcinogens – Are made up of hydrogen and carbon – Emitted by motor vehicles, dry cleaning • Particulates, small particles – Smallest are most dangerous to lungs Figure T01: Trends in Air Pollutant Concentrations in the United States from 1990 to 2007 Figure B01: Lead and crime rate Adapted from Nevin, Rick, Environmental Research 104 (2007): 315-336 Secondary Air Pollutants • Are produced in chemical reactions with primary air pollutants • Present harder-to-solve problems than primary air pollutants • Include acid deposition and photochemical oxidants (smog)/ozone Water Vapor, Clouds and Aerosol • Warmer temperatures will lead to more water vapor in the atmosphere because saturation vapor pressure increases with temperature – Extra water vapor is more greenhouse gas – A positive feedback loop, more warming – Enhanced cloudiness complicates this scenario • Human activity leads to changes in cloudiness – Contrails from aircraft – Aerosols from ships contribute to cloudiness – Aerosols from cities, ships act as CCN Figure 03: Ship tracks Courtesy of SSEC and CIMSS, University of Wisconsin-Madison Figure 04: Contrails-- satellite Courtesy of GeoEye and NASA. Copyright 2010. All rights reserved. Figure 05: Saturation vapor pressure varies as a function of temperature Acid Deposition • Can be acid rain, snow, fog, dew, or dry • Formed when oxides of nitrogen and sulfur combine with water vapor or liquid water to produce nitric acid and sulfuric acid • In water, allows toxic heavy metals to leach out and contaminate drinking water • Damage to structures, make lakes toxic Figure 06: pH scale Courtesy of EPA Figure 07: pH of rain Photochemical Oxidants/Smog/Ozone • Irritates eyes, nose, throat; causes coughing chest pain, and shortness of breath, aggravates asthma and bronchitis • Forms when sunlight acts on a combination of hydrocarbons, oxides of nitrogen, and oxygen • Ozone is the main component, with PAN and formaldehyde The Stratospheric Ozone Hole • Is reduced amounts of ozone over the Antarctic in the decades since 1955 • Occurs in the Antarctic spring • Is the result of the chlorine in CFCs • Occurs because • The Antarctic atmosphere is very cold • Has polar stratospheric clouds • The polar vortex prevents mixing • Should improve in the next 50-100 years Figure 08: The observed ozone minimum over Antarctica between 1955 and 2009 Modified from: GSFC/NASA Figure 09: The daily minimum ozone values between 40°S and the South Pole Modified from: GSFC/NASA Figure 10: The annual average size of the ozone hole Modified from: GSFC/NASA Desertification • Is a spread of a desert region • Is due to climate change • Is due to human impacts on the land – – – – Overgrazing Deforestation without reforestation Diversion of water from a fertile region Farming on unsuitable land (terrain, soil) • Vulnerable areas include fringes of Sahara desert, the Aral Sea, Lake Chad (West Africa) Figure 11: Aral Sea, 1989 to 2008 Courtesy of the University of Maryland Global Land Cover Facility/Landsat and MODIS/NASA Urban Heat Islands • Increased temperatures compared to rural surroundings • Greatest effect in summer and during the night • Due to human activities – – – – – Industrial activity Thermal properties of buildings and roads Evaporation of water Air conditioning and heating Transportation Figure 12: Urban heat island – conceptual model Figure 13A: Urban heat Island – satellite Courtesy of Robert Simmon, based on data from the National Land Cover Database and Landsat 7/NASA Figure 13B: Urban heat Island – satellite Courtesy of Robert Simmon, based on data from the National Land Cover Database and Landsat 7/NASA Figure 14: Heat island – London Adapted Chandler T.J. The Climate of London. Hutchinson, 1965 Figure 15: Magnitude of urban heat island Courtesy of T. R. Oke, The University of British Columbia Figure B02: Urban Heat Island and precipitation Adapted from Shepherd, J.M., et al., Agronomy Monograph 55, (2010): 129 and J. Aitkenhead-Peterson and A. Volder (ed.). Urban Ecosystem Ecology. American Society of Agronomy, 2010 Global Warming is a Fact!!! • Over the past 2 decades the global average surface temperature has increased noticeably. • A trend involves a steady change in one direction—upward for global average temperature. • Not every location and/or every region shows the identical pattern. Figure 16: Temperature departures from the global mean temperature over land since 1880 Source: NASA/GISS Figure 17: The annual temperature changes of the past 50 years Courtesy of GISS/NASA More Observations of Global Warming • • • • • • Widespread retreat of nonpolar glaciers Thinning of arctic sea ice Decreased N Hemisphere snow cover Increase of global mean sea level Longer growing season in NH Shortened duration of ice cover on NH lakes Figure 18: Sea level rise Source: Intergovernmental Panel on Climate Change, "Climate Change 2007,” The Fourth Assessment Report, Working Group 1, Figure 5.13; Red curve from: Church and White, 2006; Blue curve from: Holgate and Woodworth, 2004; Black curve from: Leuliette et al., 2004 Figure 19: SeaWiFS Ocean biology Courtesy of GeoEye and NASA. Copyright 2010. All rights reserved. Figure 20: Sea Ice change Source: National Snow and Ice Data Center Figure 21: Snow cover change Courtesy of Riccardo Pravettoni, UNEP/GRID-Arendal Figure 22: Lake Mendota ice cover Source: Wisconsin State Climatology Office Figure 23: Winter Temperature changes Courtesy of NOAA/NCDC Greenhouse Gases and Global Warming • Greenhouse gases include carbon dioxide, water vapor, methane, CFCs and others • Concentrations of carbon dioxide have increased by 25% since the 19th century, and increase by 0.5% per year • More energy is trapped in Earth’s atmosphere • Feedbacks are very important • Scientists rely on complex computer models of climate Global Warming and the Oceans • Oceans absorb energy trapped by increased amounts of greenhouse gases • Vertical motions in the atmosphere are very sensitive to temperature – Climate change can accelerate rapidly if global warming affects convection in the oceans • Oceans are full of life, which will be affected by global warming • Sea level is rising due to thermal expansion and melting of ice sheets over land Global Warming and the Cryosphere • Cryosphere is the portion of Earth’s surface covered by ice • The cryosphere is shrinking – Mountain glaciers are shrinking – Arctic ice has thinned and covers a shrinking area at the end of summer – The Greenland ice sheet is melting rapidly • Earlier snowmelt inhibits storage of water • Lakes freeze/melt later/sooner and lose water through evaporation Global Warming and the Biosphere • Biosphere comprises all of Earth’s living organisms • Tundra plants/animals are very sensitive to changes in snow cover and temperature • Gardeners notice changes in hardy zones related to global warming The IPCC • IPCC is the Intergovernmental Panel on Climate Change (over 1000 scientist) – Formed by the United Nations’ World Meteorological Organization (WMO) and the Environment Programme (UNEP) in 1988 • Writes reports that describe our current knowledge about climate change, based on published scientific literature • Has 90% confidence that observed temperature rises are due to humans